Carbon black and other metals, powders, fibers, ionic polymers, and other additives have been incorporated in a wide variety of manufacturing formulations for antistatic protection. Carbon black which is readily available in many grades either as a powder or aqueous dispersion can be conveniently employed whenever black coloration is not objectionable as in tires, mats, video disks, etc.
Dispersions of powders in liquids can be obtained commercially. The dispersions of powders such as carbon black in plasticizer are custom made commercially.
Pony et al., U.S. Pat. No. 4,097,656, discloses polymerizable plastics which can be blended with conductive carbon black specially prepared by treatment with hydrocarbons under pressure and then heated.
Martin et al., U.S. Pat. No. 4,228,050, discloses molding video disks containing about 15% carbon black having a high surface area and a high proportion of voids in which electrical current flows in a highly efficient manner in an otherwise nonconductive polymer matrix.
Charles, U.S. Pat. No. 4,374,760, discloses improving conductivity of a resin with carbon black by adding an organic titanate coupling agent to the composition.
McCraken et al., U.S. Pat. No. 4,629,585, discloses a foamable antistatic polymer composition containing 5% conductive carbon black having a BET surface area of at least 500m.sup.2 /g.
A recent article by Arie Calahorra--Investigation of Electrical Resistivity--Pigment Volume Concentration Relationship in Carbon Black-Filled Conductive Paint, Journal of Coatings Technology, Volume 60, No. 757, February 1988, discusses conductivity changes in a carbon black/PVC polymer matrix with carbon black loadings of 15 to 37%. A high grade conductive carbon black (Ketjenblack EL-DJ600 from AKZ0 Chemie, the Netherlands) was reported to be the best conductive filler employed in these tests.
White and transparent conductive powders for use as antistatic additions in PVC and polypropylene are described in an article by Yoshizume and Wakabayashi of Mitsubishi Metal Corporation, Conductive Powders Adapt to Today's Product Decors, Plastics Engineering, March 1987, pp. 61-64. Based on data provided in this article, about 57% by weight titanium dioxide coated with antimoney doped tin oxide will provide 10.sup.9 ohm/sq. surface resistivity for a plastic film.
Thus, while a large number of publications existed prior to the present invention on various ways to employ conductive particles such as carbon black in vinyl plastics such as PVC, the prior publications failed to describe means or measures to easily utilize carbon black without rendering the composition black or how to employ low amounts of carbon black, e.g., using less than 4 to 5% by weight of carbon black in a vinyl plastic matrix.
In contrast to the practice and experience heretofore, the present invention utilizes considerably lower amounts of carbon black and enables dilution of the carbon black pigment with nonconductive white pigment while providing fully adequate static dissipative vinyl sheets and films.